Circuit interrupter



Dec. 20, 1949 o. B. cuRRY l CIRCUIT INTERRUPTER Filed Aug. 15, 1946 INVENTOR O//Ver .5. Carry, (i BY/ /LAfw/,

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WITNESSES: 4P/M5 Patented Dec. 20, 1949 CIRCUIT IN TERRUPTER Oliver B. Curry, Wichita, Kans., assigner to Westlnghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 15, 1946, Serial No. 690.6215

13 Claims. (Cl. 200--113) l This invention relates generally to electric circuit interrupters, and more especially to such interruptersvwhich are adapted to replace fuses.

To properly protect apparatus, such as transiormers. which are subject to relatively light overe .approximate the thermal characteristics of apparatus of the type mentioned above, and one object of this invention is to provide a novel circuit interrupter wherein opening of the circuit is initiated by a bimetal element.

Another object of this invention is tov provide a novelvcircuit interrupter of the type described wherein the circuit interrupting contacts are nor.. mally held, closed against an opening bias by a renewable fusible strain element connected in shunt circuit relation with said contacts, and the contacts are initially separated by an overloadresponsive means.

Another object of this invention is to provide in a circuit interrupter of the type described, a y novel structural relationship of current carrying contacts and shunt connected fusible strain element for normally holding said contacts closed against a contact-opening bias.

' Another object of this invention is to provide in a circuit interrupter of the type described, novel means for adjusting the current-responsive element of the interrupter for selecting the current values at which it willrespond to open e the circuit.

Still another object of this invention is to provide in a device of the type described, a novel arrangement of the parts to enable ready replacement of the renewable element thereof.

-Another object of this invention is to provide a circuit interrupter having a renewable fusiblev element tocause circuit interruption to occur butwhich does not normally carry any appreciable current and is caused to fuse by other currentresponsive means.

These and other objects of this invention will become more apparent upon consideration of the following detailed description of a preferred embodiment thereof when taken in connection with the attached drawing, in which:

Figure 1 is a substantially central longitudinal 2 section through a circuit interrupter constructed in accordance with this invention; and

Fig. 2 is a top plan view of the interrupter shown in Fig. 1.

The embodiment of the invention which is disclosed herein is illustrated as being contained within a tubular holder 2 of insulating material, preferably a molded insulating material, with a lower portion 4 which is relatively small in diameter compared to a shorter upper portion 6, The upper end of holder 2 is provided with a terminal cap 8 which may be of any desired electrical conducting material such as copper or a copper alloy, and this cap is held in place by a semi-circular retaining spring I II having the ends thereof directed inwardly to engage in apertures provided in the ilange of cap 8 and in the upper end of large diameter portion 6 of the tubular holder. A terminal conductor I2 may be secured to cap I0 in any desired manner, such for example, as by soldering or the like.

A sleeve Il'having a reduced upper end which extends through a substantially central aperture in terminal cap 8 is adapted to be secured to the cap as by soldering or brazing. The lower end of the opening through sleeve Il is smaller than the opening through the sleeve, as shown at I6, and the restriction at I6 is flared in opposite directions, for a purpose to be described. A generally U- shaped bimetal element I8 has the upper leg thereof secured to the lower end of sleeve III, as by soldering or the like, and is provided with a ilared opening 24 forming a continuation of the opening I Ii in the lower. end of sleeve I4., Bimetal element I8 is formed in the usual manner of a pair of laminations 20 and 22 of diierent metals secured together as by welding or the like. Outer lamination 20 of the bimetal element should be of a material having a relatively higher coefficient of thermal expansion than the material comprising inner lamination 22, so that upon heating o! the bimetal element the leg portions thereof will approach each other.

The lower leg of bimetal element I8 is provided with a relatively large opening 26 and has secured to the under side thereof a contact member 28, preferably of an alloy which is resistant to arclng. Contact 28 is provided with a flared opening 30, the outer end of which coincides with opening 26 in the bimetal element.

The small diameter portion! of holder 2 is provided with. a liner tube 82 of an insulating material which is capable of evolving an arc-extinguishing gas when in proximity to an electric arc, such for example, as fiber, a synthetic resin or the like. Liner tube 32 may be inserted in portion 4 Aof the holder with a tight-nt up against stop washer 34 which may be molded directly in portion 4 of the holder 2. A contact rod 38 which is elongated in form is provided normally in the small diameter portion of the holder, with an enlarged contact head 38 secured at the upper end thereof to engage contact 28 of bimetal element I8. Contact rod 88 is provided with a substantially central longitudinally extending bore 48 which extends not only through contact rod 38, but through contact 38 as we ll, and is alinged with opening 88 in contact 28, openings 28 and 24 in bimetal element I8, and with opening I8 through sleeve I4. A fusible strain wire 42 which is of a material having a relatively high electrical resistance extends through bore 48 and the openings in contacts 28 and 38 and through the openings in the bimetal element and through sleeve I4. Sleeve I4 on cap 8 is adapted to have threadedly mounted therein an adjusting sleeve 48 which has a central bore 44 for accommodating strain wire 42, with adjusting sleeve 48 being provided exteriorly of` the holder above terminal cap 8 with an adjusting disk 48 having certain in dicia thereon, herein illustrated as the numbers I through 8 equally spaced about the periphery thereof. Above disk 48 on adjusting sleeve 48, and below the lower end of contact rod 38, strain wire 42 is provided with abutment sleeves 58 secured thereto, for example, as by being crushed thereon, by some sort of crimping tool.

The lower end of contact rod 38 where it projects from holder 2 has a sleeveK 52 secured thereon in any desired manner, for supporting adisk 84 above sleeve 52. A coil compression spring 58 is adapted to react between stop washer 34 and disk 54 t0 normally bias the contact rod and its contact 38 downwardly in a direction away from contact 28 to open the circuit when released. Sleeve 52 on the contact rod may include an oiset portion 58 in which a terminal conductor 88 may be secured as by soldering or the like. Preferably adjusting disk 48 is provided with a number of substantially semi-circular notches 82 spaced around the periphery thereof and corresponding in number to the numerals on the disk, and these notches are -adapted to cooperate with a lock screw 84 adapted to be threaded into a threaded opening in terminal cap 8.

The circuit through the interrupter illustrated on the drawing extends from the upper terminal conductor I2, through terminal cap 8 and sleeve I4, through bimetal element I8 to its contact 28, then to movable contact 38, contact rod 38 and sleeve 52 Ito the other terminal conductor 80. It will be observed that strain wire 42 is in parallel with part of the circuit described above in that it is electrically, as well as mechanically, associated with terminal cap 8 by way of adjusting disk 48 and sleeve I4, and is similarly associated With contact rod 38, so that it is in shunt circuit with contacts 28 and 38 as well as bimetal element I8. Inasmuch as strain wire 42 is of a relatively high resistance material, normally substantially all of the current flow through the interrupter will be in the first described circuit, namely, through bimetal element I8 and contacts 28 and 38. Very little, if any, current will iiow through strain element 42. The principal function of the strain element 42 is to hold movable contact 38 in engagement with contact 28 under predetermined contact pressure. Because of the material comprising bimetal element I8 and the particular U-shape thereof, it has suillcient ref siliency that in the positions oi' the parts shown' the element will tend to approach the upper leg,

thus relieving contact pressure on contacts 28 and When contact 28 actually separates from contact 38, Ithe circuit through the contacts is interrupted, leaving only the shunt circuit through strain wire 42 connected between terminals I2 and 88 of the interrupter. Accordingly at this time, that is, when contacts 28 and 38 actually separate, a large amount of current flows through strain wire' 42 which will immediately fuse and permit compression spring 58 to rapidly move contact 38 downward through the holder. In its downward movement, contact 38 will rapidly elongate the arc which will be exposed to the walls of liner tube 32 which, in turn, will evolve an arc-extinguishing gas. The rapid elongation of the arc coupled with the action of arcextinguishlng gas thereon will quickly extinguish the arc to interrupt the circuit. .It will be noted that contact 38 is larger in diameter than the opening in stop washer 34, so that at the end of circuit-opening movement the lower end of contact; rod 38 will project a relatively great amount from the lower end of holder 2, to thereby indicate that the interrupter has operated to interrupt the circuit. It will be noted that by the provision of strain wire 42 extending substantially centrally through contacts 28 and 38, it not only is of assistance in centering these contacts but when the strain wire melts, .the arc will have to transfer to contacts 28 and 38 because at that time, it will be substantially centrally located with respect to these contacts.

In assembling the interrupter described above and illustrated in the drawing,1 or in reloading the interrupter after it has operated to interrupt the circuit, it is only necessary to replace strain ,wire 42 in a manner such that bimetal element I8 is stressed an amount suiiicient to exert pressure on contacts 28 and 348. One way in which this may be done is to remove retaining spring I0 so that terminal cap 8 may be removed, whereupon strain wire 42 with its lower sleeve 50 a+- tached thereto can be inserted into the lower end of holder 2, through bore 40 in the contact rod, and through the openings in contacts 28 and 38. The wire may be then easily threaded through the tapered openings in the bimetal element, sleeve I4 and screw 48, whereupon terminal cap 8 can be replaced on the holder and fastened by retaining spring I 0. The upper sleeve 58 can then be placed on the strain wire and contact rod 38 pushed upwardly into holder 2 until it engages contact 28. The upper sleeve 50 could then be secured to strain wire 42. With the strain wire 42 in place, adjusting disk 48 may be rotated until the point is reached where contacts 28 and 38 are just touching. The adjusting disk 48 can then be screwed outwardly a predetermined numberfof turns corresponding to the indicia thereon to give a predetermined deformation of bimetal element I8. Any excess in length of strain wire 42 may be clipped off at the ends and the interrupter is ready to be put back in service. In order to prevent accidental disturbance of the setting of the device, it is desirable to use a locking screw 84 for the purpose of retaining adjusting disk 48 to the position to which it has been adjusted.

Another method of assembling strain wire l2 is to thread the strain wire down through the assembly from the top until upper sleeve 50| rests either on adjusting screw I8, or this screw may be eliminated and sleeve ill may rest directly on terminal cap 8. The entire mechanism may then be supported on a crimping tool for the lower sleeve 50 and a predetermined weight attached to the protruding lower end of strain wire I2 to subject contacts 28 and 38 and the mechanism under predetermined stress and give the bimetallic element it a certain deformation. Lower sleeve 50 may be then crimped to strain wire I2 and the excess of the wire clipped off.

It will also be apparent that the size of strain wire l2 is far from critical since normally this wire only needs to oppose mechanical forces exerted by spring 56 and the bimetal element, since it carries substantially no current. Consequently, the size of strain wire I2 does not efl'ectthe current rating of the device. It is believed apparent from the foregoing that the interrupter disclosed herein generally comprises separable contacts which are biased apart but normally held engaged under predetermined contact pressure by a fusible strain element; however, the strain element does not determine the rating of the' device, this being determined by a separate element (bimetal element il) which operates at the desired current to cause strain wire 42 to melt by opening contacts 28 and 38 and thereby causing allof the excess current to flow through strain wire I2. I

Having described a preferred embodiment of the invention in raccordance with the patent statutes, it is-desired that the invention be not limited to this particular device inasmuch as it will be readily apparent to those skilled in this art that many modifications and changes lmay be made in this particular construction without departing from the broad spirit and scope of the invention.` Accordingly, it is desired that the invention be'interpreted as broadly as possible and that it be limited only as required by the prior art.

I claim as my invention: 1. In Va circuit interrupter, separable contacts which are biased apart, fusible strain means nor.-

mally maintainingsaid contacts in engagement 'against saidbias, said strain means being electrically connected in shunt relation with said contacts and being of relatively high resistance, and motive means connected with oneofsaid contacts and' responsive to excessive current flow through said contact-sto initially separate said contacts to thereby transfer said current to said strainl means and cause fusion of said strain means and release of said contacts for separation by said bias to interrupt the circuit.

2. In a circuit interrupter, separable contacts which are biased apart and atleast one of which is resiliently mounted, fusible strain means normally maintaining said contacts in engagement against said bias while stressing said resilient current flow through said contacts for causing said strain means to melt, and means associated contacts and being of relatively high resistance, and a bimetal element connected with one of vsaid contacts and responsive to excessive current dow through said contacts to initially separate said contacts to thereby transfer said current to said srain means and cause fusion of said strain means and release of said contacts for separation by said bias to interrupt the circuit.

4. In a circuit interrupter, separable contacts which are biased apart, fusible strain means normally maintaining said contacts in engagement against said bias, said strain means being positioned adjacent a lateral surface of at least the movable one of said contacts so as to be engageabie by at least one of said contacts upon relative lateral movement thereof to thereby maintain said contacts properly centered, and means responsive to excessive current flow through said contacts for causing said strain means to melt.

5. In a circuit interrupter, separable contacts which are biased apart, fusible strain means normally maintaining said contacts in engagement against said bias, said strain means being electrically connected in shunt relation with said contacts and being of relatively high resistance, means responsive to excessive current flow through said contacts to initially separate said contacts to thereby transfer said current to said strain means and cause fusion of said strain means and release of said contacts for separation by said bias to interrupt the circuit, andy at least a portion of said strain means positioned intermediate said contacts at least upon said initial separation of said contacts so that the arc formed upon fusion of said strain ferred to said contacts.

6. In a circuit interrupter, separable contacts one of which is biased for movement away from the other, the other one of said contacts beingf mounted on a resilient bimetal element which the other contact.

7. In a circuit interrupter. separable contacts one of which is biased for movement away from the other, fusible strain means normally holding said one contact in engagement with the other of said contacts, means responsive to excessive with said strain means for manually adjusting the contact pressure .exerted by said othercontact'. l,

8. In a circuit interrupter, a tubular holder o! insulating material, closure means for the top of said holder and including a terminal for the 'i interrupter, one contact mounted in said holder and electrically connected with said terminal, an arc passage in a portion of said holder, a movable contact mounted for movement through said ablecontact arid-saidl holder fornormally holding said contacts engaged under predetermined pressure, means responsive to excess current flow through said contacts to cause said wire to melt,

the bottom of said holder being open, and means.

limiting circuit opening movement of said movable contact to an amount wherein a part movmeans will be transable therewith projects a predetermined amount from the lower end of said holder.

9. In la circuit interrupter, a tubular holder of insulating material, closure means for the top of said holder and including a terminal for the interrupter, one contact mounted in said holder and electrically connected in series circuit relation with said terminal, an arc passage in a portion of said holder, a movable contact mounted for movement through said arc passage into and out of engagement with said one contact, ysaid movable contact being biased to move away from said one contact, a fusible strain wire connected between said movable contact and said terminal for normally holding said contacts engaged under predetermined pressure, and a 'bimetal element responsive to excess current flow through said contacts and being connected to said one contact to cause said one contact to move away from the other contact.

10. In a circuit interrupter, a tubular holder of insulating material, a terminal cap for one yend of said holder, separable contactsin said holder one of which is mounted on said cap and the other being biased to move through said holder away from said one contact, a strain wire normally connecting said movable contact and cap to hold said movable contact in engagement with said one contact, and motive means connected with said one contact and being responsive to excess current ilow through said contacts to cause said one contact to move away from the other contact.

1l. In a circuit interrupter, a tubular holder of insulating material, a terminal cap for one end of said holder, separable butt contacts in said holder one of which is mounted on said cap and the other being biased to move through said holder away from said one contact, a strain wire extending through openings in said cap and contacts, abutments secured on said wire to engage said cap and movable contact, respectively, for normally holding said movable contact in engagement with said one contact, and means responsive to excess current flow through said contacts to cause said one contact to move away from the other contact.

12. In a circuit interrupter, separable contacts one of which is mounted on a bimetal element which responds to excess current in the circuit to move said one contact away from the other of said contacts, said other contact being biased for movement away from said one contact, and a. fusible strain element mechanically and electrically connecting said contacts to normally hold them in engagement, whereby on excess current in the circuit said bimetal element separates said one contact from the other to cau-se all of said current to flow through and melt said strain element whereupon said other contact moves under the iniluence of its bias away from said one contact to interrupt the circuit.

13. In a circuit interrupter, separable contacts one of which is mounted on a bimetal element of resilient material which responds to excess current in the circuit to move said one contact away from the other of said contacts, said other contact being biased for movement away from said one contact, a fusible strain element mechanically and electrically connecting said contacts to normally hold them in engagement, whereby on excess curret in the circuit said bimetal element separates said one contact from the other to cause all of said current to flow through and melt said strain element whereupon said other contact moves under the iniluence of its bias away from said one contact to interrupt the circuit, and means for adjusting one of said elements to vary the pressure on said bimetal element and thereby vary the current value at'which said bimetal element separates said one contact from the o her.

OLIVER B. CURRY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,294621 Conrad vFeb. 18, 1919 1,848 152 Bieger Mar. 8, 1932 2,277,619 Wallace Mar. 24, 1942 

